The attempted dehalosilylation reactions between AlX3 (X = Cl, Br) and P(SiMe3)3 in toluene in 1:1 mole ratios afforded only the adducts Cl3Al·P(SiMe3)3 (I) and Br3Al·P(SiMe3)3 (II), respectively. Compounds I and II were characterized by 1H, 13C, 27Al, and 31P solution NMR spectroscopy, as well as partial elemental analysis. In addition, the solid state structures of the toluene solvates of I and II were determined by single-crystal X-ray analysis. Characterization revealed that the solid solvated adducts I and II are isostructural and their crystals are isomorphous. In each compound, the Al and the P atoms reside in tetrahedral environments, with each X3Al·P(SiMe3)3 (X = Cl, Br) molecule associated with one interstitial toluene molecule in the crystals. These adducts are noteworthy in that they possess extremely short, essentially equal AlP bond lengths [for I: AlP = 2.392(4) Å, and for II: AlP = 2.391(6) Å], which are the shortest found to date in aluminium-phosphorus molecular species. © 1994.